The genetics of atresia is being explored in several inbred strains of mice and their F1 heterozygote crosses. Initial experiments have identified differences in the rates of atresia in several inbred mice strains as well as their F1 heterozygotes. Two families with familial human premature ovarian failure are being studied. The mechanism of premature ovarian failure in galactosemia is being explored. Experimental animal studies demonstrate that exposure to galactose during pregnancy can decrease oocyte number.